On the Specificity of Phospho-N-acetylmuramyl-pentapeptide Translocase

Phospho-N-acetylmuramyl-pentapeptide translocase (UDP-MurNAc-Ala -y~Glu-Lys -DAla -nAla: undecaprenylphosphate phospho-MurNAc-pentapeptide transferase) catalyzes the initial membrane reaction in the biosynthesis of peptidoglycan.In addition, the enzyme catalyzes the exchange of [3H]uridine monophosphate with the uridine monophosphate moiety of UDP-MurNAc-pentapeptide.A specificity profile towards the peptide subunit of UDP-MurNAc-pentapeptide has been established for the exchange and transfer reactions catalyzed by the translocase from Sfaphylococcus aureus Copenhagen.A good correlation between V,,,JK, in the transfer reaction and R,,,,JK,,, in the exchange reaction was observed.On the basis of glycine substitution, the enzyme has a high specificity for L-alanine in position 1 (RI) and n-alanine in position 4 (R4) and a low specificity for n-alanine in position 5 (R,).For example, when compared with UDP-MurNAc-Ala-DGlu-Lys-DAla-DAla, glycine replacement in either R1 or Rq results in a Q-and 15-fold decrease in V,,,/K,, respectively.In contrast, glycine substitution in R5 results in only a IS-fold decrease in V,,,f Km.These results are further supported by comparing UDP-MurNAc-Ala-DGlu-Lys-nAla-DAla, -Ala-DGlu-Lys-nAla, and -Ala-DGlu-Lys.For UDP-MurNActetrapeptide a 4-fold decrease in Vmax/K,,, was observed whereas a 7'7-fold decrease was found for the -tripeptide.Replacement of both R, and R4 by glycine reduces R,,,jK, 135-fold.The translocase has a low specificity for the diamino acid in Rs.Substitution of lysine with mesodiaminopimelic acidresults in a 1.5-fold decrease in R,,,/K,,, and with ornithine in no change.The established specificity profile of the translocase is consistent with the in vivo effects of elevated concentrations of glycine on the growth of S. aureus Copenhagen (HAMMES, W., SCHLEIFER, K. H., AND KANDLER, 0. (1973) J. BacferioZ., 116, 1029-1053).Thus, it is suggested that the translocase has a key role in selecting analogs of UDP-MurNAc-Ala-ynGlu-Lys-DAla-DAla for peptidoglycan synthesis.